1. Technical Field
The present invention relates to linear motion bearing and, more particularly, to linear motion bearing assemblies made up of bearing segments for longitudinal movement along a splined shaft.
2. Background of Related Art
The present invention is directed to an improved linear motion bearings assembly for use on a splined shaft. In particular, the improvements relate to biased linear motion bearing assemblies of the type which support a carriage or a pillow block for linear movement along an elongated splined shaft. These bearing assemblies can either be of the open type or the closed type.
Typical linear rolling bearing assemblies include a series of rolling elements moving about a circulation path which circulation path is formed in the periphery of a track member and a surrounding and enclosing bearing cover confining the rolling elements in their recirculation path. In order to achieve an accurate linear motion, the axis of the bearing assembly must be precisely aligned with the desired direction of motion along the supported structure. In addition this precise alignment also minimizes skewing forces acting on the bearing assembly, which skewing forces tend to reduce the load/life performance of the bearing assembly.
Installation of such bearing assemblies on a supporting structure (i.e., shaft, splined shaft, guideway or rail) typically involves precision machining of locating surfaces in order to properly align the bearing assembly on the supporting structure. Such bearing assemblies are typically installed in sets, each comprised of a number of variously facing bearings such as to engage a series of surfaces on the supporting structure (i.e., such as above and below a supporting surface and/or along a lateral edge of a supporting surface). In such instances it is usual to provide a bearing adjustment for enabling precision adjustment of the bearing assembly on the supported structure and also for establishing a proper bearing pre-load by adjusting an opposing bearing assembly for reasons well known to those skilled in the art. In such installations, considerable precision machining of the supported structure is necessitated which is difficult and expensive to accomplish on the supporting structures.
Additional prior art bearing assemblies typically include an outer housing and at least one ball retainer dimensioned for insertion into the outer housing. The rolling element retainer has at least one ball track in a loop configuration for containing and recirculating bearing balls therein. The ball tracks typically include open portions which facilitate a load transfer from a supporting shaft to a load bearing structure such as load bearing plates operatively associated with either the ball retainer or the outer housing while return portions of the ball tracks permit continuous recirculation of the bearing balls through the ball tracks during linear motion.
In some embodiments, the ball retainer is formed as a monolithic element with the ball tracks integrally incorporated therein. See, U.S. Pat. No. 3,767,276 to Henn. This structure, however, is difficult to efficiently manufacture because of the complex molds required. Also, these ball retainers, prior to insertion into a mounting carriage or outer housing are necessarily open and thus exposed to ambient conditions and contaminants such as dust and dirt. Such exposure could deleteriously affect the operation and life of the bearing assembly as well as the support structure on which it moves.
Self-contained linear bearing units are also known in the art. See, e.g. U.S. Pat. No. 4,815,862 to Mugglestone et al. This unit, while representing a marked improvement in the art, still requires the use of end caps to engage the load bearing plates of the bearing segments. Further, the load bearing plates must be precisely machined to properly inter-fit with the end caps. This configuration adds to the expense and complexity of the bearing.
The load bearing structure may be in the form of integral elements formed on an inner radial surface of the outer housing. Typical bearing assemblies utilizing load bearing structures formed in the outer housing are shown, for example, in commonly owned U.S. Pat. No. 5,046,862 to Ng, the disclosure of which is incorporated herein by reference.
In lieu of integral load bearing structure, separate load bearing plates may be used to transfer loads from the supporting shaft. These load bearing plates are longitudinally oriented in association with the ball retainer so as to engage at least those bearing balls in direct contact with the support shaft. These load bearing plates may also be configured to be axially self-aligning by providing structure which permits the plates to rock into and out of parallelism with the longitudinal axis of the ball retainer. See, for example, commonly owned U.S. Pat. No. 3,545,826 to Magee et al. Individual load bearing plates may be expanded transversely so as to engage bearing balls in corresponding adjacent load bearing tracks. In this form, parallel grooves are formed in the underside of the plates to guide the bearing balls while they are in the load bearing portion of the ball tracks. See, for example, U.S. Pat. No. 3,951,472 to Schurger et al.
Accordingly, it is an object of the present invention to provide a linear motion bearing segment which can be easily and efficiently manufactured.
It is another object of the present invention to provide a linear motion bearing assembly having a rolling element retainer and outer housing which are easily fabricated using engineering polymers, powder metal or insert molding.
It is a further object of the present invention to provide a low cost linear motion bearing assembly having a high load bearing capacity and having self-aligning capability.
It is yet another object of the present invention to provide a bearing assembly which eliminates the need for extremely high precision rolling element/guideway (rail) bearing assemblies and their resultant expensive manufacturing costs.
These and other highly desirable objects are accomplished by the present invention in a linear motion bearing assembly having a plurality of rolling element tracks and individual bearing plates arranged in a rolling element retainer and enclosed by a low cost outer housing which serves to protect the rolling elements, rolling element tracks and load bearing plates without having to transmit loads from the bearing rolling elements to the carriage block into which the bearing assembly is mounted.
Objects and advantages of the invention are set forth in part herein and in part will be obvious therefrom, or may be learned by practice with the invention, which is realized and attained by means of instrumentalities and combinations pointed out in the appended claims. The invention comprises the novel parts, constructions, arrangements, combinations, steps, processes and improvements herein shown and described.